In a brake apparatus of a vehicle, such as an automobile, when a driver depresses a brake pedal, braking operation is performed. The stroke of the brake pedal is transmitted to a piston of a master cylinder such that the piston moves over a corresponding stroke. The master cylinder converts the stroke to a braking hydraulic pressure corresponding to a treading force applied to the brake pedal, whereby a braking force corresponding to the braking hydraulic pressure is generated.
In general, a brake apparatus of a vehicle, such as an automobile desirably has a nonlinear characteristic in terms of transmission of brake pedal stroke and treading force. Conventionally, brake pedal apparatuses having different structures have been proposed so as to attain a nonlinear characteristic in terms of transmission of brake pedal stroke and treading force. For example, Japanese Patent Application Laid-Open (kokai) No. H11-115699 discloses a lever-ratio-variable-type brake pedal apparatus.
In such a lever-ratio-variable-type brake pedal apparatus, since the lever ratio is changed by means of a link mechanism including a rocking link and a connection link, a relatively large space is needed so as to allow motions of the links. Further, since the respective lengths and interrelation of the links univocally determine a change in the lever ratio, the manner in which the lever ratio changes is limited. Therefore, the transmission characteristic associated with motion or force cannot be set as desired over a wide range. Notably, the above-described problem is not limited to the lever-ratio-variable-type brake pedal apparatus, and is present in other conventional motion transmission apparatuses in which the transmission characteristic for motion or force is changed by means of an ordinary cam mechanism or the like.